Re: encoding a float

Ulrich Eckhardt <>
Tue, 27 Mar 2007 10:43:28 CST
hurcan solter wrote:

Hi all, I am trying to convert a float value to a octet stream for
transmission, I came up with solution like

float deneme=3.14156789;
float deneme2=0.0;
    vector<unsigned char> vec; //this is my buffer can con contain
                   other things besides this float

int* val=reinterpret_cast<int*>(&deneme); // gives me jeebies

Right. There is no reason for reinterpret_cast here, and in particular not
to an int*. The standard guarantees that you can access the memory of an
object via a char pointer, so using a char pointer would work. Then, you
copy sizeof(float) elements, don't assume that a float has size 4!

it works, but i am not sure that this is the Right Way to do, I
wonder if there is a safer or cleaner way? I tried memcpy to treat
the vector as if an array it didn't work out well( although, It
should work right?)

It does work:

  // serialize
  vec.resize(sizeof deneme);
  memcpy( &vec.front(), &deneme, sizeof deneme);

  // deserialize
  assert(vec.size() >= sizeof deneme);
  memcpy( &deneme2, &vec.front(), sizeof deneme);

HOWEVER: you still have a big problem there and that is that the layout of
floating-point values in memory is not portable between different
architectures. Therefore, I'd suggest you use a text-based format which
makes it much easier to transfer the data between different machines.


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